In the paper Brian Knutson proposes a biochemical basis behind sexuality and gender. It's a hard read but Brian gets close to what I presume we all want to read when he says:

Animal research has indicated that the male and female poles of brain sexuality reflect extremes of a gradient that allows for many intermediate types

Brian then goes on to assert that at least 4 sexes exist in the world - man within man, woman within woman, man's mind within the body of a woman, and a woman's mind within the body of a man. He claims the details for this have been worked out in lower animals, suggesting that similar principles also operate in humans.

BUT Brian is still a long way from suggesting a scientific basis for the common assertion by trans women that they have a female brain trapped in a male body.

The focus of Brian's work is lust and sexuality - and the variations he has mapped out talk only to sexual preferences.

Various forms of homosexuality and bisexuality are promoted if "errors" occur in the various control points of these biological processes

So there is a hint of an explanation of sexual diversity. But I didn't find any clues to what might cause gender variance as widely experienced in the transgender community. The vast majority of transgender people I have met over the years do not express a feminine gender in order to facilitate having sex with males. A few do, but the evidence of the majority indicates that there is more at play than just lust and reproductive sexuality.

If further research confirms that there is a change to the brain that results in a feeling of male or female gender (as opposed to male or female sexuality) then we must also be wary of assuming that those with a feminine gender identity must have a feminine gender brain.

There is an early (and woefully inadequate) study of transexual brains that concluded exactly the opposite. Although male and female brains can be distinguished, the tested trans women were found to have male brains. The study details are here:

cercor.oxfordjournals.org/content/21/11/2525.full.pdf+html

"The present study does not support the dogma that male-to-female transsexuals have atypical sex dimorphism in the brain but confirms the previously reported sex differences in structural volumes, gray, and white matter fractions,"

If you subscribe to the view that there is a masculine and feminine brain (and everything in between) then Dr Brian Knutson's neuroanatomical observations on small furry animals may provide a possible explanation. As the animals can't talk, the observations were on their sexual behaviour (p230) which he then suggests may apply in humans. This leads the article (through references to homosexuality) to suggest mismatches of femininised brains with masculinised bodies leads to sexual variety. Or in Brian's words (p232)

The fact that male and female brains have distinct but related psychosocial properties allows sexual urges to become quite complicated in the real world

Studies on homosexual and hetero sexual males have suggested that there is a difference in their brains (Savic et al. 2005; Berglund et al. 2006; Savic and Lindstrom 2008). Brian Knutson would I expect embrace this as confirming his views that variation in sexual attraction can be traced to changes in brain development.

But nothing in all this explains how two very feminine women can be attracted to each other in a lesbian relationship (with feminine brains they should be attracted to men). Nor does it model the lack of correlation between attributes that Knutson suggests as feminine (nurturing and social motivation) and expressed sexual preference (love and lust).

The arguments for feminine and male brains whilst encouraging us to accept sexual variety as normal, barely scratch the surface in explaining why we exhibit (and presumably feel) different degrees of femininity. I subscribe to the view that sexual variance (as embraced in the Gay/Lesbian/Bisexual community) is distinct from the gender variance we all experience. If gender and sexual variance are distinct and independent then it is unlikely that one simple mechanism will account for both. The dimensions of gender seem designed to defeat any model based on a linear progression of brain types.

But in the absence of any better explanation of gender you can of course believe what you want. You can build your understanding of yourself around a concept of "unconscious sex" as proposed by Julia Serano. And because it is unconscious you can't be expected to know anything about it - let alone explain it to anyone else!

If however your gender faith looks for scientific proof - then be aware that brain sex research is riddled with more holes than Swiss Cheese.

Love and lust can be far more enjoyable if you don't have to analyse it!